The present invention relates to an optical type of pickup apparatus for optically reading the signals recorded on the signal reading medium and particularly an optical type of pickup apparatus which controls the posture of the objective lens.
There are apparatuses which read the signals from the signal recording medium using an optical type pickup apparatus. A DC player is one of many of these types of apparatuses. The CD player reproduces digital signals formed on the signal faces of the compact discs (CD) which have projections called pit. The CD player must control the optical beam in the optical axis direction, the so-called focusing direction, using a focusing control operation to correctly converge the optical beam on the signal face on the disc. The optical beam is produced from the optical type pickup apparatus. Also, it is necessary to perform a tracking controlling operation for controlling the optical beam in the radial direction of the disc, the so-called tracking direction, to cause the optical beam to follow the signal track on the disc.
Normally an optical-type pickup apparatus has an objective lens disposed within a lens holder. A tracking coil and a focusing coil are wound on the lens holder. Control signals are input to the tracking coil and the focusing coil in order to perform tracking control and focusing control. Thus, the optical type pickup apparatus was required to support the lens holder so that it might freely move in the tracking direction and the focusing direction in accordance with the input control signals.
Shown in FIG. 1 of Japanese Laid-Open Patent Application Tokkaisho No. 57-127934 Publication is an example of an optical type pickup apparatus as described hereinabove. A support member, composed of viscometric elastic member, supported the driven member as the lens holder. As the support member was elastic, torsion was caused by the force to be applied in the axial direction of the support member so that the posture of the lens holder could not be retained properly.
Also, a cantilever type support apparatus was conventionally known wherein, for example, four steel wires were disposed in parallel with one end of the steel wire being secured to the frame and the other end thereof being secured to the lens holder. The cantilever type apparatus using the steel wire, did not have elasticity in the axial direction as the steel member. The support apparatus of this type had an advantage because the posture of the lens holder could be kept with respect to the force to be applied in the axial direction.
However, the cantilever type of support apparatus using the steel material (wire) had to retain the weight of the lens holder only with the wire. If the wire is made thicker to increase its strength, stiffness of the wire becomes larger, and the resonance frequency of the wire becomes higher. Thus, the device is vulnerable to vibration. Due to the unbalance of the driving force, the support position of the lens holder, during the tracking controlling or the focusing controlling, was concentrated on the single side of the lens holder so that a rolling operation (rolling) was caused. Thus, the correct posture could not be retained.